1. Field of the Invention
The present invention relates to processes utilizing ionic liquids for the dissolution of various polymers and/or copolymers, the formation of resins and blends, and the reconstitution of polymer and/or copolymer solutions, along with the dissolution and blending of “functional additives” and/or various polymers and/or copolymers to form advanced composite materials.
2. Background of the Invention
The use of ionic liquids as replacements for conventional organic solvents in chemical, biochemical and separation processes has been demonstrated. Graenacher, U.S. Pat. No. 1,943,176, first suggested a process for the preparation of cellulose solutions by heating cellulose in a liquid N-alkylpyridinium or N-arylpyridinium chloride salt, especially in the presence of a nitrogen-containing base such as pyridine. However, that finding seems to have been treated as a novelty of little practical value because the molten salt system was, at the time, somewhat esoteric. This original work was undertaken at a time when ionic liquids were essentially unknown and the application and value of ionic liquids as a class of solvents had not been realized.
Ionic liquids are now a well-established class of liquids containing solely ionized species, and having melting points largely below 150° C., or most preferably below 100° C. In most cases, ionic liquids (ILS) are organic salts containing one or more cations that are typically ammonium, imidazolium or pyridinium ions, although many other types are known. The range of ionic liquids that are applicable to the dissolution of cellulose are disclosed in U.S. Pat. No. 6,824,599, herein incorporated in its entirety by reference, and in Swatloski et al., J. Am. Chem. Soc. 2002, 124:4974-4975.
Traditional cellulose dissolution processes, including the cuprammonium and xanthate processes, are often cumbersome or expensive, and require the use of unusual solvents, typically with a high ionic strength. These processes are also used under relatively harsh conditions (Kirk-Othmer “Encyclopedia of Chemical Technology”, Fourth Edition 1993, volume 5, p. 476-563). Such solvents include carbon disulfide, N -methylmorpholine-N-oxide ((NMMO), mixtures of N,N-dimethylacetamide and lithium chloride (DMAC/LiCl), dimethylimidazolone/LiCl, concentrated aqueous inorganic salt solutions (ZnCl/H2O, Ca(SCN)2/H2O), concentrated mineral acids (H2SO4/H3PO44) or molten salt hydrates (LiClO4.3H2O, NaSCN/KSCN/LiSCN/H2O).
These traditional cellulose dissolution processes break the cellulose polymer backbone resulting in regenerated products that contain an average of about 500 to about 600 glucose units per molecule rather than the native larger number of about 1500 or more glucose units per molecule. In addition, processes such as that used in rayon formation, proceed via xanthate intermediates, and tend to leave some residual derivatized (substituent groups bonded to) glucose residues as in xanthate group-containing cellulose.
Other traditional processes that can provide a solubilized cellulose, do so by forming a substituent that is intended to remain bonded to the cellulose, such as where cellulose esters like the acetate and butyrate esters are prepared, or where a carboxymethyl, methyl, ethyl, 2-hydroxyalkyl (for example, hydroxyethyl or hydroxypropyl), or the like group, is added to the cellulose polymer. Such derivative (substituent) formation also usually leads to a lessening of the degree of cellulose polymerization so that the resulting product contains fewer cellobiose units per molecule than the cellulose from which it was prepared.
Physical and chemical processing methods for treating cellulosic resources are numerous. Chemical, enzymic, microbiological and macrobiological catalysts can be used to accelerate the process under conditions selected to be thermodynamically favorable to product formation.
Chemical processes include oxidation, reduction, pyrolysis, hydrolysis, isomerization, esterification, alkoxylation and copolymerization. Chemical and enzymatic hydrolysis of cellulose is discussed in The Encyclopedia of Polymer Science and Technology, 2nd Ed, J. I. Kroschwitz (Ed in Chief), Wiley (New York), 1985. Wood, paper, cotton, rayon, cellulose acetate, and other textiles are a few examples of the broad range of cellulosic materials.
With increasing industrial pollution and consequent governmental regulations, the need to implement “green” processes to prevent pollution and waste production and to utilize renewable resources is becoming increasingly prominent. The efficiency of existing methods for dissolving and derivatizing cellulose can be significantly improved by the availability of suitable solvents for refined and natural cellulose; an example is N-methylmorpholine-N-oxide (NMMO), used as a solvent for non-derivatizing dissolution of cellulose for the production of lyocell fibers. [http://www.lenzing.com.]
It has been reported that cellulose can be dissolved in solvents describe as ionic liquids that are substantially free of water, nitrogen-containing bases and other solvents (U.S. Pat. No. 6,824,599). However, processes for producing cellulose blends and other polymeric blends with a wide range of possible polymeric components, and a wide range of properties, have yet to be fully developed.